Process and catalyst for the hydrodealkylation of alkyl aromatic hydrocarbons



United States Patent 3,277,197 PROCESS AND CATALYST FOR THE HYDRODE-ALKYLATION 0F ALKYL AROMATIC HYDRO- CARBONS Bruno Notari, San DonatoMilanese, Italy, assignor to SNAM S.p.A., Milan, Italy, a company ofItaly No Drawing. Filed Aug. 7, 1963, Ser. No. 300,621 Claims priority,application Italy, Aug. 10, 1962, 692,833 5 Claims. (Cl. 260-672) Thisinvention concerns a process and a catalyst for the catalytichydrodealkylation of alkyl aromatic hydrocarbons, and is particularlyintended for the production of benzene and naphthalene by catalyticdealkylation of methyland/0r ethyl-substituted benzenes andnaphthalenes.

The petrol industry has available petroleum fractions essentiallyconstituted by mixtures of alkyl benzenes and/ or alkyl naphthalenes, inparticular of alkyl aromatics wherein the alkyl group is methyl. Thetransformation of .these products into the non-substituted correspondingaromatics, namely benzene and naphthalene, is convenient from theeconomical point of view, and is an object of great interest in thepresent development of petroleum chemistry.

The dealkylation of methyl-aromatics can be carried out thermally aswell as catalytically, using in both cases hydrogen under pressure andat more or less elevated temperatures. The catalytic processes howeverafiord various advantages over the thermal ones, first among which theuse of more moderate temperatures; owing to the contemporaneous presencein hydrogen reactors under elevated pressure, this factor greatlyreduces the cost of the plants.

With the catalytic processes described in literature for the productionof aromatic hydrocarbons through the dealkylation of alkyl-aromatics,which generally proceed at temperatures of from 450 to 700 C., underhydrogen pressure of from 1 to 100 atmospheres, various types ofcatalysts are employed, which generally include a metal of the eighthgroup, a metal of the sixth group or their oxides supported on porousmaterials such as alumina, silica, silica-alumina. Though the catalyticmaterials employed are difierent, none of them is really quitesatisfactory. If one take into account that the hydro-dealkylationreaction tivity of the reaction, to avoid all the further losses due tocollateral reactions.

Hence it is a main object of the present invention to elevate the yieldsof dealkylated product obtainable by a process of catalyticdealkylation, through the use of a 3,277,197 Patented Oct. 4, 1966catalytic agent more selective than those known at present.

Taking into account that the speed of dealkylation of thealkyl-aromatics depends strictly on the temperature of the catalystmass, on the partial pressure of hydrocarbon and hydrogen, and on theratio between the amount of substance put to react by unit of time andunit of cat-alytic mass, namely on the space velocity, it is also adisstinct object of the present invention to improve, at equalexperimental conditions, the velocity of dealkylation, namely theconversions into dealkylated product, of course without diminishing theselectivity of the catalyst, namely keeping elevated yields. Both thesefactors tend to result in larger quantities of dealkylated product atequal load and equal technical characteristics of the plants.

- It has now been found that it is possible to attain both these resultsthrough the use of oxides or sulfides of the metals of the sixth groupsupported on alumina of high purity preferably in the eta phasecharacterized by an elevated porosity, by a surface area of about to 200m. /gr., and by an average diameter of the pores of more than 150 A.lower than 550 A. and preferably around 250 A.

To obtain these characteristics the aluminas should be prepared byparticular processes since the commercial aluminas have chemical andphysical parameters quite different from these optimal ones.

It is not known whether this particular and advantageous behaviour isrelated to the crystalline structure of the support or instead to itsphysical structure under stood as a surface area, and pore size. At anyrate it has been observed that every time an oxide or sulfide of themetals of the six group B is supported on these particular aluminas theresults are definitely better than those obtainable with commercialaluminas; from what has been said it follows that the aluminasutilizable according to the instant process cannot be tabletted or atany rate obtained through a procedure involving pressing because duringthis operation the porosity of the material is partly destroyed. Insteadit is necessary to obtain them by a procedure imparting to the finalproduct the desired chemical and physical structure, in addition ofcourse to good mechanical properties that permit the industrial usethereof.

For a certain optimal chemical and physical structure the conversionobtainable under standard experimental conditions is considerably largerthan with catalysts having difierent structure; moreover the yield isslightly improved by the convenient selection of the structure of thesupport. Modification of which, therefore, is not limited to increasingthe velocity of the hydrodealkylation reaction, which is a fundamentalfactor, for a more intensive exploitation of the catalyst systems, butalso succeeds in improving the selectivity of the reaction, minimizingthe collateral cracking reactions, which generical- 1y lead to theformation of hydrocarbons dilferent from the desired ones or to a cokedeposit on the catalyst.

, In order better to illustrate the present invention the followingexamples are reported which should not be considered as a limitationthereof; a

EXAMPLE 1 Various catalysts essentially constituted by chromium oxide onalumina were prepared by impregnation of commercial aluminas calcined at550? C. The impregnation was made with a solution of chromic acid insufiicient quantity to obtain a final product constituted by alumina 3with 16% of chromium oxide; the reduction was effected with hydrogen at300 C. The commercial aluminas utilized for this purpose were theHarshaw H-l04 alumina, and the Alcoa F-lO alumina. The character- Fromthis porous alumina a catalyst was prepared with 16% C-r O by the sameprocess followed for commercial aluminas; said catalyst will behereinafter indicated as porous alumina with 16% Cr O The catalysts sopreistics of these aluminas are reported in the following 5 pared weretested for the hydrodealkylation of toluene to table: benzene in ahigh-pressure apparatus of stainless steel. Table 1 Chemical andphysical characteristics of The temperature along the catalytic bed waschecked commercial aluminas and the differences between the variouspoints of the bed were smaller than 3 C. The results obtained aretabulated in- Table 3, in which are also reported the results PmpemesHarshaw'mm F40 obtained by utilizing two commercial dealkylatingcatalysts, the Girdler 6-41 and the C-30 of Catalyst and g tg g, g 3Chemicals Inc orosi y, .gr r Average diameter ofpores, A g1? 8% Fromthis one can observe that the behaviours of the ggg g gg hg'g;figififEIIII: I catalyst prepared according to the present invention,is definitely superior and provides higher conversions. with thecatalysts prepared from commercial alumi- A porous alumina according tothe present inventlon respect to wasdobtained in the following way: to aZolution of A1Cl3 f i g l j ii gg ifig iz g f i g's 'gbf g is a ded acooled solution of hexamet ylene tetramine gy e gg g assistan ;tiiszztttstazfiai ara a ut to an ove at C. or ours. t f end gi the i isCompletely gelified. It conversions and yields are ldentlcal to those ofthe fresh is extracted from the vessel, cut into cubes of 1 cm.sidec,atalyst whefeby prlwed that nelther during f length and put into aseparator funnel kept at by tron nor during operation there takes placea dlminutron means of a jacket in which water from a thermostat circuofi PmPemeF of the catalyst N from l1a1tes. gt is then washe1d Italydistilllled water brcctlught fto p21?) 'l gitsl fior n svhtici32135321521}; lgeltgveegtir tIl)1:h;!ai23;1 Oatt;

wit ammonia, an t e was mg is carrie on or 7 hours. At the end of thewashing, the material is put into one according to 1111? Presentlnvenflon, was made at equal an oven at 95 C. and after some hours themost of the Y 1f the 00111113118011 had been e water has beeneliminated. At this time the alumina qual welght, the catalyst preparedfrom porous alumina shows at the X-rays the prevailing structure of thewould prove to be more effective by more than 100%. bayerite trihydrate.It is put into a muflie furnace and In practice that means a furtheradvantage deriving from gradually heated up to 550 C. The alumina soobtained the use of a smaller quantity by weight of catalyst.

Table 3 HLSV, Percent of Stoichiometric Catalyst Ml. Gr. Molar H; toReaction Pressure, ml./ml., benzene in the yield (percent tolueneratiotemperature, atm. catJhr. reaction of theory 0 product (8) gr S plus 16%50 58 2 3 620 40 1 1 4 (b) claofIIIIIIIIIIIIIIIIIII 50 5011 a 620 40 150:7 3237 (c) Alcoa 1 plus 16% OM03" 50 57. 9 a 620 40 1 45. 6 99. 5 (d)Girdler-G41 50 3 620 40 1 50.5 95.3 (e) A1103 porous plus 16% r; 50 29.83 620 40 1 68.4 96.5 (f) A1103 porous plus 16% CnO; atterregeneratmg 5029.8 3 620 40 1 69.7 96.6

1 The values reported are the average values observed during the first25 hours of operation. The life of the catalyst, however, is much moreelevated has high purity and has the characteristics tabulated inEXAMPLE 2 Table 2.

Properties: Porous alumina Also in the dealkylation of themethylnaphthalenes the Crystalline structure eta catalyst according tothe present invention displayed Su f area, 2 13 higher activity thanpreviously known catalysts. By way Porosity 9 of example, in Table 4 aretabulated the results obtainedv Average pore diameter, A 263 in t edealkylation of l-methyl naphthalene with a com- Real density gr./ml.3.2 mercial catalyst (C-30) and with the catalyst prepared Apparentdensity gr./m1. 0.9 from porous alumina.

Charging density kg./ liter 0.5

Table 4.-Hydr0dealkylati0n of l-methylnaphthalene Catalyst Ml. Gr. Te fia t i re, Pressure, Ell /21 1 nagl ithii l ri ln y i l jg g I C.atmospheres cat/hr. the reaction of theory mixture o-ao a0 50. 1 540 401 so. 1 97, 7 A; porous plus 16% 01703.... 50 29. 8 540 40 1 87. 5 98. 7

Hence also in the hydrodealkylation of methyl naphthalene to naphthalenethe use of the catalyst according to the present invention isconsiderably more convenient.

EXAMPLE 3 Clearly too elevated an average diameter of the pore leads toa diminution of the velocity of dealkylation. Hence an interval remainsdefined, as to the average diameter of the pores, between 150 and 550A., in which the 5 catalytic activity passes through a maximum. The goodcharacteristics found in the catalyst prepared I claim: irom porousalumina which chromium oxide are observed 1. A process for obtainingbenzene and naphthalenes also if on the porous alumina are depositedother oxides with elevated conversions from methyl and ethyl derivaorsulfides of the VIth Group. For instance in Table 5 tlves by means ofcatalytic hydrodealkylation, comprising are tabulated the resultsobtained with a catalyst pre- 10 bringing a charge containing saidderivatives into contact, pared by impregnating the porous aluminaaforeat temperatures between 500 C. and 650 C. and presdescribed withmolybdenum sulfide. sures between 1 and 100 atmospheres, with a catalystTable 5 Percent of Stoichiometric Catalyst M1. Gr. Temperature,Pressure, HLSV, m1./m1., benzene in yield, percent C. atmospherescat/hr. the reaction of theory product A1203 porous plus MOS; 50 30. 1620 40 1 70. 3 95. 7

EXAMPLE 4 comprising a material selected from the group consisting ofThe elevated specific activity of the catalyst described in the presentinvention permits the utilization of catalytic compositions containingminor quantities of chromium oxide, as can be seen in Table 6 whereinare reported the oxides and sulfides of metals of the VIth group Buniformly distributed and supported on alumina of high purity, of:porosity not lower than 0.5 ml./gr., and not higher than 1.8 ml./ gr.and with pores having an average results obtained with a catalyst having6% of chromium diameter between 150 and 550 70% 0f POres oxide. ing adiameterbetween 150 and 550 A.

Table 6.-Hydrodealkylati0n of toluene Percent of Stoichiometrie CatalystM1. Gr. Temperature, Pressure, HLSV, m1./ml., benzene in yield, percent0. atmospheres cat/hr. the reaction of theory product A1 0; porous plus6% CnOa 50 28. 5 620 I i 1 68.8 95.9

This constitutes a further economical improvement due to the use ofminor quantities of chromium oxide on the catalyst.

EXAMPLE 5 A catalyst was prepared with aluminum having low density,having an average pore diameter of 550 A. and a total porosity of 1.8mL/gr. to determine Whether a further increase in the average diameterof the pores leads still to an increase of the velocity of dealkylation.

The results are reported in Table 7.

Table 7.-Hydrodealkylati0n of toluene Percent 01 Stoichiometrle CatalystM1. Gr. Temperature, Pressure, HLSV, m1./m.l., benzene in yield, percentC. atmospherers cat/hr. the reaction of theory product Low density A1303plus 16% References Cited by the Examiner UNITED STATES PATENTS3,053,760 9/1962 Henke et al 252-466 X 3,067,128 12/1962 Kimberlin eta1. 252-465 X 3,075,022 1/ 1963 Gammon et al 260-672 3,116,345 12/1963Slaymaker 252-439 X 3,204,007 8/1965 Mukai et al. 260-672 DELBERT E.GANTZ, Primary Examiner.

C. R. DAVIS, Assistant Examiner.

1. A PROCESS FOR OBTAINING BENZENE AND NAPHTHALENES WITH ELEVATEDCONVERSIONS FROM METHYL AND ETHYL DERIVATIVES BY MEANS OF CATALYTICHYDRODEALKYLATION, COMPRISING BRINGING A CHARGE CONTAINING SAIDDERIVATIVES INTO CONTACT, AT TEMPERATURES BETWEEN 500*C. AND 650*C. ANDPRESSURES BETWEEN 1 AND 100 ATMOSPHERES, WITH A CATALYST COMPRISING AMATERIAL SELECTED FROM THE GROUP CONSISTING OF OXIDES AND SULFIDES OFMETALS OF THE VITH GROUP B UNIFORMLY DISTRIBUTED AND SUPPORTED ONALUMINA OF HIGH PURITY, OF POROSITY NOT LOWER THAN 0.5 ML/GR., AND NOTHIGHER THAN 1.8 ML./GR. AND WITH PORES HAVING AN AVERAGE DIAMETERBETWEEN 150 AND 550 A., 70% OF THE PORES HAVING A DIAMETER BETWEEN 150AND 550 A.